We propose to study (1) determinants of seroconversion in the non-intravenous-drug-abusing (NIVDA) steady heterosexual partners of two population groups; a) patients in the Bellevue Hospital Methadone Maintenance Treatment Program (MMTP) and b) hospitalized intravenous drug abusers (IVDA's) with AIDS and (2) development of disease in seropositive partners. The first part of the study will focus on determinants of seroconversion in heterosexual partners. These include: 1. the protective effect of condom use, 2. the importance of frequency and type of sexual contact, 3. the effect of HIV-related illness in the index patient, and 4. the predictive value of HIV antigen capture in the index patient on seroconversion in the sexual partner. The second part of the study will assess factors relevant to the development of disease in seropositive sexual partners. These factors include: 1. the importance of the health status of the index patient and the following factors in the partner; 2. the role of the level of immune function, 3. the importance of other (non- intravenous) drug use and history of sexually transmitted infections, 4. the role of co-infection with HTLV 1, HTLV 2, Herpesviruses and hepatitis, 5. the predictive value of antigen capture, and 6. the predictive value of antibody to HIV core antigen. A total of 200 partners will be entered into the study, 100 from each population group. Partners will be interviewed and examined. Laboratory studies will include serologies for HIV, HTLV 1, Hepatitis B, Hepatitis Delta, HSV 1, HSV 2, CMV, and EBV. Those who test positive for HIV will also be tested specifically for antibody to the HIV envelope and core proteins. All partners will be tested for HIV antigen and quantitation of lymphocyte subsets will be performed. Univariate and multivariate logistic regression analysis will be used to separately analyze risk of seroconversion and disease development in each group.